The invention concerns a method for welding electric conductors such as litz wires using ultrasound, especially litz wires among one another to produce transit or end nodes, or litz wires with a support, wherein the conductors are introduced into a compression chamber bounded by at least two bounding elements and are welded after the compression chamber is closed, wherein ultrasound is applied via a first element such as a sonotrode and the conductors to be welded are subjected to pressure via the first element or a second element such as a counter electrode, and wherein a characteristic magnitude of the compression chamber is measured. The invention also relates to a method for the quality verification of conductors welded in a compression chamber of an ultrasound welding device, especially litz wires welded into a transit or an end node, or litz wires welded on a carrier, whereby the conductors to be welded are arranged at least between a first element applying ultrasound, such as a sonotrode, and a second element, such as a counter electrode, whereby the conductors are subjected to pressure via the second or the first element. Finally the invention relates to a method for verifying the quality of welded conductors, especially welded litz wires such as transit or end nodes or litz wires welded on a support.
In the ultrasound welding of a node, several litz wires, such as copper conduits, which in turn consist of several strands, are introduced into a compression chamber, compressed, and then brought into relative vibration toward one another by ultrasound. The friction of the strands among one another leads to a welding of the surfaces so that a solid node exists after the welding. During the compression and welding, the volume of the compression chamber diminishes. This change in volume can be measured by displacement pickups and used as a comparison value for checking quality. The strength of the node is the decisive quality criterion for the process of ultrasound welding.
In order to determine the strength of corresponding nodes, the nodes can be measured destructively or non-destructively, by pulling or peeling, via a type of hardness testing (splice checker).
One method for regulating the course of the process for quality control in the ultrasound welding of workpieces can be found in EP-B-0 208 310. In this method, in activating the ultrasound energy, a sonotrode of an ultrasound welding device is lowered onto a workpiece lying on an anvil, whereby a null balance takes place when the sonotrode is placed upon the workpiece, in order to subsequently activate the sonotrode and to allow a desired deformation path to pass through.
A method for the ultrasound welding of thermoplastic materials is known from SU-A-757 337, in which the depression depth of the sonotrode, and therewith the deformation of the workpieces during the welding process, is recorded via a displacement pickup directly applied to the sonotrode. The welding process is terminated with a sign change of the second temporal derivation of the path signal.
A method, a device, and a system for producing connections to integrated circuits are described in DE-A-2 149 748. In order to attain improved connections, the introduction of force onto a tool, but also the energy acting upon it, is controlled via the deformation of the parts to be connected, via a displacement pickup.
A regulation of the welding process using ultrasound is known from FR-A-2 302 172 in which the speed of the depression motion of a sonotrode during the welding process is recorded, compared with specified limit values, and the energy supply to the sonotrode is restricted when adjustable thresholds are exceeded.
In WO-A-95/10866 A method and a device for welding conductors are described, with which a defined welding can take place independently of cross section, even when conductors of different cross sections are successively welded in random order. For this, a characteristic magnitude of the compression chamber is measured after compression of the conductors to be welded.
In order to be able to adjust the height and width of a compression chamber that accommodates conductors to be welded, and to be able to set the respective cross section automatically, devices are known, such as those disclosed in EP-B-0 143 936 or DE-C-37 19 083.